Mobile terminals for wireless communication are used in different communication standards such as global system for mobile communications (GSM), digital cellular system (DCS), and Universal Mobile Telecommunications System (UMTS). Each of these communication standards cover and use different frequency bands. For a mobile terminal to be used with different standards, it needs to be capable of transmitting, receiving and processing signals on different frequency bands. Radiated performance is also a critical parameter in mobile communication. Particularly with mobile phones, radiated performance is dependent on the use of the phone.
User effects, such as the way a user holds a mobile terminal relative to the positioning of the internal antenna elements may affect the over-the-air performance of the device. The near field of the antennas such as hands and head strongly influence the antennas. In modern mobile terminals, two or more antennas can be used for communication to the base station. Since a transmitter may use only one antenna, total radiated power (TRP) can be improved by using switched diversity, or simply “using the best antenna.” For example, the best antenna for transmitting may be used by simply swapping the RF channels between the platform front-end-module (FEM) and the antenna. This technique is known as antenna swapping. A given wireless electronic device may swap from using one group of antennas with its transmission chains to using a different group of antennas.
Wireless communication devices, such as WIFI 802.11N and LTE compliant communication devices, are increasingly using Multiple Input-Multiple Output (MIMO) antenna technology to provide increased data communication rates with decreased error rates. A MIMO antenna includes at least two antenna elements.
MIMO technology may offer significant increases in data throughput and/or transmission range without the need for additional bandwidth or transmit power. It can achieve this due to the ability of MIMO to obtain higher spectral efficiency (more bits per second per hertz of bandwidth) and/or reduced fading.
MIMO based systems allow the use of a variety of coding techniques that take advantage of the presence of multiple transmit and receive antennas. For example, wireless communications performed over a MIMO channel can use beamforming, spatial multiplexing and/or diversity coding techniques.
One technique is called downlink carrier aggregation, or simply carrier aggregation (CA). CA is a technique where two or more frequency bands are used together in order to increase the total (aggregated) bandwidth. For downlink CA, four receivers, two at each frequency band (main+diversity) are working at the same time but with only one transmitter. In some cases where a harmonic of the transmitted signal falls directly in the receive band of the other carrier, there will be extremely high linearity requirements on the circuit path between the transmitter and the antenna. In particular, extreme linearity requirements will be put on the antenna swapping switch (DPDT) when the antenna swapping technique is combined with CA.